Very few kids are going to enjoy a roadtrip, no matter what car they're in.

True, I would never take my 335i on a road trip anyway. It's black=rock chips, I don't want to rack up miles on my turbos, and I don't want the inside wrecked by eating and stuff during the car ride. So that leaves me to taking my wifes car on any trip we take. And I enjoy having a larger vehicle on road trips. More room, higher up on the highway, pack more stuff without having to plan it out, carry bikes without worrying about scratching my paint. Stuff like that. A bigger car in the family is just a given to me.
PLUS: we have no spare tire, means i have to carry that in the trunk also=less space. Our cars are not very road trip friendly in my mind.